Aerosol paint compositions are well known but have used volatile organic solvents as the carrier and propellant for the film-forming polymer. Toxicity and flammability problems arise from the use of such organic solvents and governmental regulatory authorities are moving towards severe restrictions on the use of organic solvents in such compositions.
There is, therefore, a need to provide a non-flammable aerosol-based paint composition which is also non-toxic and at the same time able to provide a satisfactory paint film on a substrate surface. The applicant is aware of one prior attempt to meet this need and this prior art attempt is described in Japanese patent publication No. 23640/1979 published Feb. 22, 1979.
As set forth therein, an aqueous aerosol coating composition of low flammability and toxicity is provided. Water is used as the resin solvent, alone or in conjunction with other solvents, to form a stock solution containing 5 to 20 wt.% of resin. The resin is formed by copolymerizing four essential monomers in critical proportions, predominating in acrylic or methacrylic acid esters, followed by partial neutralization with ammonia and/or an amine.
The stock solution is incorporated into an aerosol container for propulsion therefrom using any convenient propellant. Proportions of stock solution to propellant are disclosed to be 70 to 30 wt.% propellant and 30 to 70 wt.% stock solution. The Examples of this prior art disclose the use of mixtures of fluorocarbons and dimethyl ether as the propellants, which produces a two-phase liquid system, in view of the hydrophobicity of the fluorocarbon. Two phase systems introduce problems with dispersing uniform quantities of active component, such as is essential with paint formulations.
It is further disclosed in this prior art that the formulations described in the Examples have residual flammability, although decreased as compared to volatile organic solvent-based systems. The problem of flammability, therefore, has not been overcome by this prior art.
The prior art formulation uses a very specific acrylic resin in the paint composition. Attempts by the applicant to reproduce this resin following the procedures outlined in the Examples thereof have been unsuccessful. As described in the prior art, the resin is chemically an unmodified acrylic resin and, as such, is moisture sensitive when formed as a film.
The prior art of this Japanese patent publication, while achieving some improvement over the organic solvent-based aerosol paint compositions, nevertheless, has not provided a non-flammable aerosol paint composition which may be readily sprayed onto a substrate surface to form a durable paint film thereon.
The Japanese patent publication discloses dimethyl ether as a possible propellant component for the stock solution, but indicates no preference thereto, nor any reason why this material should be selected as compared to other propellants. Indeed, as already noted, in the preferred embodiments of the prior disclosure, namely the Examples, a combination of dimethyl ether and fluorocarbons is used.
It has also been previously suggested elsewhere to use dimethyl ether as a propellant. U.S. Pat. No. 1,800,156 discloses the use of dimethyl ether alone as the propellant for a large variety of materials and paints are mentioned. U.S. Pat. No. 3,207,386 discloses the utilization of a combination of dimethyl ether and water as a propellant for a wide variety of products including paints, the proportions being chosen to provide a homogeneous solution of the dimethyl ether and water as the propellant and this restriction results in a composition consisting of 5 to 35% by weight of dimethyl ether and 95 to 65% by weight of water. No other solvent or propellant components are used in this prior art composition.